Control arrangement for hydraulic systems

ABSTRACT

A hydraulic system comprising a plurality of working circuits each including a control valve and a fluid motor, a control signal pressure is selected from a working pressure of one or more working circuits; and this control signal pressure is applied to a valve that is effective to modify the operation of one of the working circuits. The hydraulic system includes a priority valve incorporated into well-known Delta P valves for applications to hydraulically-controlled equipment, such as shovel loaders, the priority function being desirable in this connection to provide pressure or flow priortiy to the bucket cylinders while the bucket is being filled.

United States Patent [191 [451 Oct. 30, 1973 McMillen, deceased CONTROL ARRANGEMENT FOR HYDRAULIC SYSTEMS [75] Inventor: Kenneth G. McMillen, deceased, late of New Castle, 1nd. by Leanne S. McMillen, administratrix [73] Assignee: Borg-Warner Corporation, Chicago,

Ill.

22 Filed: July 13,1972

21 Appl. 1101271304 [52] 11.8. C1 91/412, 91 /414, 214/762 [51] Int. Cl ..F15b 11/16 [58] Field of Search 1., .i 91/412, 414

[56] References Cited UNlTED STATES PATENTS 2,737,196 3/1956 Eames 91/412 X 2,892,311 6/1959 VanGerpen 60/422 3,179,120 4/1965 Erickson et 91/414 UX e 1- El 4% 44a 501 44 McAlvay et a1. 91/412 X Byers 91/412 X Primary Examiner-Edgar W. Geoghegan AttorneyDonald W, Banner et al.

[57] ABSTRACT A hydraulic system comprising a plurality of working circuits each including a control valve and a fluid motor, a control signal pressure is selected from a working pressure of one or more working circuits; and this control signal pressure is applied to a valve that is effective to modify the operation of one of the working circuits. The hydraulic system includes a priority valve I incorporated into well-known Delta P valves for appli- \cations to hydraulically-controlled equipment, such as shovel loaders, the priority function being desirable in this connection to provide pressure or flow priortiy to the bucket cylinders while the bucket is being filled.

20 Claims, 6 Drawing Figures LIFT ARM CONTROL P CONTROL sum 2 OF 3 PAIENTEBum 30 ms was PAIENIEDIICI 30 ms SHU'I 3 OF 3 CONTROL ARRANGEMENT FOR HYDRAULIC SYSTEMS SUMMARY OF THE INVENTION This invention relates to an improved control arrangement for hydraulic systems.

The present invention is directed to and has for its principal objects the provision of an improved control mechanism for hydraulic systems that include a plurality of working circuits where each working circuit in cludes its own control valve and fluid motor. An operating pressure, or working pressure, is taken from one working circuit and is used as a control signal pressure, or operating pressures are taken from a plurality of working circuits and the highest instantaneous working pressure is selected by logic means to be the control signal pressure. This control signal pressure is applied to a pressure responsive mode valve that is effective to change the operating mode of one of the working circuits. This mode valve changes the operating mode of the one working circuit by restricting or blocking fluid connections made by the control valve of the one working circuit or by establishing and blocking fluid connections with other portions of the hydraulic system separately from the functioning of the control valve. The logic system may be adapted to select a second control signal pressure; and this second control signal pressure may be used to modify the operation of the mode valve by means of a threshold increaser. The threshold increaser responds to this second control signal pressure to change the magnitude of the first control signal pressure to which the mode control valve responds. Although the primary use of the threshold increaser is to increase the response or threshold pressure of the mode valve, the threshold increaser can also be adapted to decrease the threshold pressure of the mode valve or to occlude operation of the mode valve by increasing the threshold pressure to a value above the highest available value of the first control signal pres sure. The effective output of a variable pump system or of a fixed pump system with a bypass valve can also be controlled by either one of the control signal pressures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of the improved control arrangement for an hydraulic system and including two control valves in cross-section, a mode valve, a parallel logic system, and a fixed displacement pump;

FIG. 2 is a schematic view of .a modification of the control arrangementshown in FIG. 1;

FIG. 3 is a schematic view of the control arrangement shown in FIGS. 1 and 2 but employing a variable displacement pump;

FIG. 4 is a schematic view illustrating another embodiment of the mode valve shown in FIGS. 1 and 2, said valve being partly shown in cross-section;

FIG. 5 is a schematic view illustrating the improved control arrangement and its application to a shovel loader; and

FIG. 6 is a schematic view of amodification of the mode valve shown in FIG. 5.

The present invention comprises a control arrangement for a hydraulic system having a plurality of working circuits each consisting of a control valve and a fluid motor, and a control signal pressure is taken from one or more of the working circuits. This control signal pressure is a working pressure of one of the control valves; and it is selected from the working circuit(s)' by the use of a logic system which includes at least one control port in a control valve; and itrnay include one or more shuttle valves having three ports.

This control signal is used by a mode valve to change the operation of one working circuit by modifying the ability of the control valve (in. this one circuit) to control its fluid motor. If the mode valve is connected in series with a control valve, it modifies that control valves ability to establish fluid communication between the hydraulic system and its fluid motor. If the mode valve is connected in parallel with a control valve, it modifies that control valves ability to isolate its fluid motor from the hydraulic system.

DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION SHOWN IN FIG. 1

Referring to FIG. 1, the supply section as. illustrated includes a fixed displacement pump 10, with pressure controls in the form of a differential pressure bypass valve 11, and a relief valve 12. Fluid sumps l3 andl3a for pump 10 are also shown. A first control valve 14 is supplied with fluid pressure from pump 10 via conduits 15, 16 and 17 to inlet port 20. Exhaust fluid is returned to sumps 13b and from exhaust ports 21a and 21b via conduits 22a and 22b. Control valve 14 supplies pressurized fluid to a first fluid actuated device or fluid motor 23 via work ports 24a and 24b and conduits 25a and 25b.

The operation of control valve 14 is conventional and well-known in the art, except for its control by ports 26a and 26b and parallel logic system 27 and their operation, as will be described later. Load check .30.is standard in operation in that it allows flow from inlet port 20 to pressure chamber 31; but it will not allow re verse flow.

Control valve 32 includes valve spool 33 in workin section 34 which is identical to valve spool 35 in control valve 14. However, control valve 32 includes pressure-actuated mode valve 36 that optionally includes all of the elements inside the rectangular section indicated by the dash line that designates mode valve 36, as shown. Control valve 32 receives pressure fluid through conduits 15, 16 and 37 to inlet port 40. Pressure fluid is directed to and returned from fluid motor 41 via work ports 42a and 42b and conduits 43a and 43b. Fluid is exhausted from control valve 32 via exhaust ports 44a and 44b to sumps 13d and 13e via conduits 45a and 45b.

Control valve 14 and fluid motor 23 can be consid ered as .a first working circuit that controlsthe bucket tilt on a shovel loader (not shown); and a second control valve32 and second fluid actuated device or fluid motor 41 can be considered as a second working circuit that controls the movement of the lift arms (not-shown) on the same shovel loader. Referring again to FIG. 1, the mode valve 3618111- cluded in valve body96 of controlvalve132 and is connected in series betweenpump l0 and pressure chamber 46 of working section 34 of controlvalve 32. Thus,

mode valve 36 is able to restrict fluid flow from pump 10 to lift arm fluid motor 41;, thereby giving priority operation to bucket fluid motor 23. More particularly,

mode valve 36 includes spool bore 47 having mode valve inlet chamber 50-and outlet chamber 48 thatis a portion of pressure chamber 46. 'A :movable valving element 51 controls the fluid communication path between inlet chamber 50 and outlet chamber 48, the path being opened when element 51 moves to the left thereby allowing flow from chamber 50 to chamber 48 via reduced diameter portion 52 of element 51. Element 51 is spring-pressed to the right to a first position by spring 53 which serves as a resilient force means or bias force means. Reduced diameter portion 54 serves as a stop to limit movement of element 51 to the right. Guide portion 55 helps to align element 51 in bore d7. Element 51 is actuated to the left of the first position, as shown, to a second position allowing fluid flow from chamber 50 to chamber 48. The projected ends of portions 54 and 55 form a first fluid responsive area 57 at the right end of element 51; and the projected end surfaces of the left end of element 51, including spring recess 56, form a second fluid responsive area.

Fluid pressure from pump is applied to chamber 57 via conduits 15, 16 and 37, inlet port 40, chamber 50, and spool passage 60. This fluid pressure is effective to develop a force in chamber 57 which is proportional to the magnitude of the fluid pressure and the combined projected end areas of portions 54 and 55.

A control signal pressure is applied to the second fluid responsive area via control signal port 61 and chamber 62. Thus, element 51 is differential pressure actuated by the relative magnitude of the fluid pressures applied to the two ends of element 51 via chambers 57 and 62, by the relative areas of the two projected ends of element 51 if there is a difference in the diameters of the two ends, and by spring 53, if a spring is necessarily included.

Referring again to FIG. 1, mode valve 36 may optionally include a threshold increaser functionally effective to increase the differential pressure required to move element 51 from the first position to the second position. Threshold increaser piston 63 is slidably fitted in bore 64 and divides bore 64 into chamber 65 and sump chamber 66. The periphery of piston 63 may be provided with any suitable seal to prevent fluid leakage between chambers 65 and 66. Sump chamber 66 is communicated to sump 13d via hole 67, exhaust port 44a and conduit 45a. Piston 63 is limited in its travel to the left by stop portion 71a thereby cooperating with plunger 72 to set the assembled length of spring 53 and the minimum differential pressure required to move element 51 to the left.

Piston 63 is pressure actuated to the right by a control signal pressure supplied to threshold increaser port 73 and chamber 65. This may be the same or a different control signal pressure than that which is supplied to control signal port 61. Movement of piston 63 to the right is limited by stop portion 71b of piston 63. Since piston 63 has a fluid responsive area in chamber 65 larger than the projected end area of either plunger 72 or element 51, piston 63 is effective to move plunger I 72 to the right to increase the compression of spring 53 and thereby to increase the differential operating pressure, or threshold pressure, of mode valve 36 even if the same magnitude of fluid pressures are introduced into control signal port 61 and port 73.

In the example of using the mode valve to give priority to tilting of the bucket of a shovel loader, the working pressure of the fluid motor that controls the lift arms of the loader is used as the control signal pressure and will be designated B. This control signal pressure B is in conduit 91; and the control signal supply means consists of a logic system means and a conduit means.

The logic system means includes occluder means, fluid actuated poppet means, and attenuator means. In FIG. 1, the logic system is designed as parallel logic system 27.

The occluder means includes control port 26a interposed between work port 24a and exhaust port 21 of control valve 14; and control port 26b is interposed between work port 241) and exhaust port 21b. Valve spool 35 is effective to isolate control ports 26a and 26b from their respective work ports 24a and 24b and exhaust ports 21a and 211) when spool 35 is in the neutral position, as shown. Spool 35 is effective to connect either control port 26a or 26b to its respective work port 2411 or 24b when the selected work port is connected to chamber 31 by spool 35.

Connection of either control port 26a or 26b with its respective work port 24a or 24b is made by moving land 75a or 75b into its respective work port 24a or 24b, the shorter effective length of the land 75 thereby allowing fluid to flow from chamber 31 to the selected work port 24a or 2417 as well as allowing fluid to flow from the same work port 24a or 24b to its control port 26a or 2617.

Thus, it can be seen that control ports 26a and 26b cooperate with spool 35 to block or to occlude the working pressures of work ports 24a and 24b from conduits 76 and 77 thereby providing the function of a mechanically actuated control signal occluder means.

Check valves 81, 82 and 83 function as a parallel connected fluid actuated poppet means. Check valves 81 and 82 are connected to control ports 26a and 26b by conduits 76 and 77. Check valve 83 receives a fluid pressure from a pump or other source (not shown) via conduit 85. Check valves 81, 82 and 83 select the highest fluid pressure from conduits 76, 77 and 85-and deliver this fluid pressure to conduit 91 as control signal pressure B.

The logic system, that produces control signal pressure B, is incapable of reverse flow because of the use of the parallel connected check valves 81, 82 and 83 as the fluid actuated poppet means. Thus, control signal pressure B in conduit- 91 cannot decrease when the pressure levels of the fluid in conduits 76, 77 and 65 decrease. Therefore, an orifice 84 is formed in conduit 92 connecting conduit 91 and sump 13f to function as a limited flow control signal attenuator or attenuator means.

The hydraulic system of FIG. 1 includes a second logic system which produces a control signal pressure hereinafter designated as A in conduit 93 and which includes control ports a and 80b, conduits 88 and 89, check valves 86, 87 and 90, attenuator or orifice 94, and all of the components that are parts of first logic system 27.

The second logic system selects the highest fluid pressure from conduits 91, 88 and 89 which contain the fluid pressures of control signal pressure B, control port 80a and control port 8017. Thus, the first and second logic systems form a logic system that provides two separate control signal pressures. One of these control signal pressures being selected from all of the control ports 26a and 26b, and 80a and 80b, and conduit on the basis of the relative values of instantaneous pressures therein; and the other of these control signal pressures being selected from only a part of these working pressures; so that at least one of these working pressures is used in the selection of both control signal pressure A and control signal pressure B.

OPERATION OF, THE CONTROL SYSTEM OF FIG.

Referring to FIG. 1, in the operation of the control system, one or both of the control signal pressures may be used to control mode valve 36 and to provide various other functions. v

The mode valve can function as a priority valve sensed by flow. in explanation, control signal pressure A in conduit 93 is supplied to chamber 62 and to the second fluid responsive area of movable valving element 51 via control signal port 61; and the system pressure is applied to'chamber 57 and to the first fluid responsive area of element 51, so that these first and second areas, with the fluid pressure applied to them cooperate with spring 53 to control the positioning of element 51 of mode valve 36.

Mode valve 36 effectively functions to give priority to the bucket tilting function of control valve 14 as follows: assuming spool 35 of control valve 14 to be in its neutral position, as shown, and control, ports 26a and 26b being isolated from work port-s 24a and 24b, then the working pressure of neither port is transmitted to parallel logic system 27. Assuming that no signal pressure is supplied in conduits 85, 88 and 89, then no control signal pressure is delivered to control signal port 61, and any residual pressure in conduit 93 and chamber 62 is attenuated by orifice 94, so that the system pressure applied to chamber 57 and the first fluid responsive area is able to move element 51 tothe left compressing spring 53 and opening a fluid path from chamber 50 to chamber 46. Thus, mode valve 36 does not'restrict the operation of lift arm control valve 32 when bucket control valve 14 is not being actuated and valve spool 35 is in the neutral position.

When control valve 14 is slowly actuating the bucket of the shovel loader then a maximum pressure dropexists from chamber 31 to the work port 24a or 24b that is being pressurized. Therefore, the control port, adja cent to the work port being pressurized, will receive a control signal pressure equal to the pressure in the work port and lower than system pressure by the amount of this pressure drop. Spring 53 is sized so that the system pressure in chamber 57 will be able to overcome the control signal pressure in chamber 62 and the load of spring 53 during metering operation of the loader bucket is described. Thus, element 51 will be moved to the left and mode valve 36 will not restrict operation of lift arm control valve 32 when bucket control valve 14 is throttling fluid to bucket actuating fluid motor 23.

When spool 35 of control valve 14 is fully actuated, very little pressure drop occurs between chamber 31 and the work port 24a or 24b that is being actuated. As a result, the control signal pressure in chamber 62is almost equal to the system pressure in chamber 57; so that the control signal pressure in chamber 62 plus the spring load of spring 53 is sufficient to move element 51 to the right against the force of system pressure in chamber 57 thereby restricting flow from chamber 50 to chamber 48 and giving control valve 14 and actuation of the bucket priority over control valve 32 and operation of the lift arms. Accordingly, it is apparent that mode valve 36 provides priority for the bucket tilt operation only when spool 35 is moved to rapidly actuate fluid motor 23.

The mode valve can also function as a priority valve sensed by pressure. More particularly, the description of operation of the mode valve as a priority valve showed that priority operation occurs only when fluid motor 23 and the bucket are being actuated with valve spool 35 fully actuated; and the mode valve then provides a priority function that is flow sensed across the variable orifice formed by valve spool 35 and cooperating portion of valve body 18 of valve 14.

The system in FIG. 1 also serves to assure operation of the loader bucket by fluid motor 23 no matter how low the working pressure of fluid motor 41 nor how high the working pressure of fluid motor 23. Operation of bucket actuating fluid motor 23 is assured as follows: when bucket control valve spool 35 is actuated, the working pressure of fluid motor 23 is obtained by control port 26a or 26b for use as a control signal pressure and transmitted to chamber 62 of mode valve 36 via the control signal pressure supply means. Movable valving element 51 is moved toward the right, to a position restricting flow from chamber 50 to chamber 46 thereby causing the system pressure in conduits 15, 16, 17 and 37 to be maintained at a value sufficient to as sure satisfactory operation of bucket control fluid motor 23.

The mode valve as described will also function'as a 7 load check. Referring again to FIG. 1, control ports a and 80b supply the working pressures of control valve 32 to check valves 86 and 87 to produce control signal pressure A in conduit 93. If the fluid pressure in conduit 37 drops below the load actuating pressure of fluid motor 41 while actuating fluid motor 41, then control signal pressure A will exceed the magnitude of the pressure in conduit 37; and control signal pressure A, as introduced into chamber 62, will force element 51 to the right thereby preventing flow of fluid from chambers 46 and 48 to chamber 50; and a load being raised by fluid motor 41, 'will not drop.

In the operation of thethreshold increaser function of mode valve 36, the control signal fluid pressure B in conduit 91 is supplied to chamber 65 where the presence reacts against the projected area of piston 63, moving piston 63, moving plunger 72, and compressing spring S3so that the difference in fluid pressures between that in chambers 57 and 62 is increased to cause element 51 to move and compress against spring 53 thereby opening chamber 50 to chamber 48. In this manner, the threshold pressure is increased. When functioning as a priority valve, an increase in the threshold pressure causes the system pressure in conduits l5, 16, 17 and 37 to be maintained at a higher value in relation to the load pressure of fluid motor 23 thereby assuring adequate pressure to overcome control valve and conduit'pressure drops and thereby to force any desired quantity of flow into fluid motor 23 without regard to the pressure losses in control valve 14 and conduits 25a and 25b.

In the operation of the bypass valve 11, it will be noted that the valve 11 includes substantially equal area actuators and 101 that serve respectively to close and to open bypass valve 11. Spring 97 exerts a force to close bypass valve 11 thereby causing bypass valve 11 to remain closed until system pressure in conduits 102 and 103 and actuator 101 exceeds the level of fluid pressure of control signal pressure A as applied to actuator 100. Actuator 104 is effective to increase the differential pressure that is required to open bypass valve 11. This type of bypass valve is explained in detail in US. Pat. No. 3,631,890 of common assignee. The significance of this type of bypass valve, when used with the threshold increaser, is that the increase in differential operating pressure of bypass valve 1 1 provides the increase in system pressure required in order that mode valve 36 may function to provide adequate pressure for control valve 32 during priority operation, as described, without the bypass pressure of bypass valve 11 being excessive during standby operation.

DESCRIPTION OF MODIFICATION SHOWN IN FIG. 2

The description of FIG. 2 is identical to that of FIG. 1 except for the control signal supply means. The differences are basically two. One difference is in the use of three port shuttle valvesfor logic system elements in the placeof the check valves of FIG. 1. The other difference'is the elimination of limited flow attenuation and its replacement by valved attenuation.

. Referring to FIG. 2, a three port shuttle valve 110 of control valve 135 is connected to control ports 26a and 26b by conduits 111 and 112. The pressure in conduit 111 or 112, whichever is higher, forces ball 113 against the opposite seat, 1 14 or 115, preventing flow from the higher pressure conduit from being'dissipated into the lower pressure conduit. The higher pressure from control port 26a or 26b is discharged from third port or output port 116 into conduit 117 which is connected to input port 120 of shuttle valve 121. Shuttle valve 121 then selects the higher pressure in conduit 117 and conduits 123 and directs this higher pressure through output port 124 and conduit 125. Conduit 125 now contains control signal pressure B comparable to pressure B in conduit 91 of FIG. 1. Control signal pressure B of conduit 125 is applied to threshold increaser piston 63 via port 73; and control signal pressure B is also applied to input port 126 of shuttle valve 127. Referring now to control valve 130, shuttle valve 131 selects the higher of the pressures from the control ports 138a and 138b of control valve 130 and delivers this pressure to the other input port of shuttle valve 127 via conduit 132.

I The output of shuttle valve 127 provides control signal fluid pressure A, which fluid pressure is discharged through dual output ports 133a and l33b into conduits 134a and 134b. Conduit 134b conducts control signal pressure A into port 61 of control valve 130 for operation of the mode valve; and conduit 134a directs control signal pressure A to bypass valve 11 to pressurize actuators 100 and 104.

The logic system utilizing three port shuttle valves 121, 127 and 131 provides control signal pressures A and B, as do the check valves of FIG. 1 provide similar control signal pressures A and-B. However, the use of three port shuttle valves allows limited flow attenuators 84 and 94 of FIG. 1 to be eliminated, which also eliminates the flow loss associated with orifice 84 that is a part of the attenuator means for control signal pressure B and orifice 94 that is a part of the attenuator means for control signal pressure A.

Referring again to FIG. 2, consider first the reverse flow operation of the logic system when the valve spools of control valves 130 and 135 are in their natural positions, as shown. Lands 136a and 136b have been cut back to open a flow path from control ports 138a and 13812 to exhaust chambers 140a and 14Gb when spool 137 is in the neutral position as shown. Thus, any fluid pressure in conduits 141 and 142 will be bled to I sump 13d or 13c. Also, any fluid pressure in conduit 132 will be bled to sump 13d or 13c because ball or poppet 143 cannot simultaneously block both ports 144 and 145. In like manner, the pressure in each conduit connected to a third or output port of a shuttle valve will be bled to one of the input ports of that shuttle valve and to a sump via a control port and an exhaust port.

Attenuation from a higher pressure level of signal to a lower pressure level of signal is obtained in a similar manner. A reversible flow path is established from the highest pressure of any of the control ports. This is true because the shuttle valves are each blocking their lower pressure input ports and the balls cannot simultaneously block the highest pressure input ports. Therefore, when the pressure level of the highest input is reduced, the excess pressure is bled off by the reverse flow to a control port.

DESCRIPTION OF MODIFICATION SHOWN IN FIG. 3

DESCRIPTION OF MODIFICATION SHOWN IN FIG. 4

Referring to FIG. 4, mode valve is a variation of mode valve 36 in FIG. 1 and the mode valve in control valve 130 of FIG. 2. Mode valve 160 differs from the mode valves of FIGS. 1 and 2 in several respects. One difference is that mode valve 160 is actuated by a single fluid pressure introduced into port 161 rather than by being operated by a differential pressure. Another difference is that mode valve 160 opens one flow passage and closes another flowpassage as its movable valving element is pressure actuated from afirst position shown to a second position. In a first operating position, as shown, a flow path is open from port 163 to port 164 and in the second operating position, port 164 is closed and port 165 is opened to port 163.

While no connections are shown to ports 163, 164 and 165, it should be understood that mode valve 160 could be connected in series with a control valve, as has been previously described; or mode valve could be connected to establish and to block fluid connections to a fluid motor separate from the control of a control valve, that is, parallel with a control valve;

Fluid used for the control signal pressure and entering atport 166 is selected by the operation of shuttle valve 167. Shuttle valve 167 is shown as selecting a control signal for actuation of threshold increaser piston 170 to illustrate the fact that the logic means can select signals from any part of the system to perform any of the functions that have been described.

DESCRiFTION OF APPLICATIONS OF CONTROL SYSTEMS TO A TRACTOR BACKHOE in EMS. 1, 2., 3 and l, a shovel loader has been used as an application of a mode valve connected in series relationship with a control valve; and it was shown that these circuits provided a priority function by restricting or blocking a fluid communication path established by a control valve.

In FIG. 5, a backhoe such as is mounted to the back of industrial or farm tractors, is shown with the im proved control systemto illustrate the use of a mode valve connected in a parallel relationship to a control valve; so that the mode valve establishes or blocks flow paths independent of the action of the control valve.

More particularly, FIG. shows, schematically, an application of the mode valve concept in which the down position of the boom and the digging forces are limited according to fluid pressures incurred during the digging cycle thereby preventing a slowing or stopping of the digging cycle.

Swing pivot post 180 is attached to pivot bracket 188 that is,- in turn, mounted to a tractor or other vehicle. Boom 181 is pivotally mounted to swing pivot post 180; and the inclination of boom 181 is controlled by fluid motor or boom cylinder and piston assembly 182 which is pivotally connected to both boom 181 and post 180. Dipper stick 183 is pivotally attached to boom 181; and the angle between the two is controlled by crowd cylinder and piston assembly 184 that is pin mounted to dipper stick 183 and boom 181. Bucket 185 is pivotally at-,

tached by pin 186 to dipper stick 183 and its rotation about pin 186 is controlled by bucket cylinder and piston assembly 187 pivotally attached to a lug 189 projecting from dipper stick 183 and to arm 190 that is attached to bucket 185.

In FIG. 5, rectangles 191a and 191b represent control ports of control valves such as control ports 26a and 26b of control valve 14 in FIG. 1; and rectangles 192a and 1921) represent work ports of a control valve such as work ports 24a and 24b of control valve 14 in FIG. 1. In like manner, the control ports and work ports of five other control valves are represented by similar sets of four rectangles.

Each set of rectangles is labeled to show which control valve it represents. The two outside sets represent the stabilizer valves and are used to control cylinders (not shown) that, in turn, control stabilizer arms (not shown) that engage the ground to stabilize the backhoe during the digging operation. Swing valve 198 controls hydraulic cylinders or arotary fluid motor (not shown) to rotate post 180 about a vertical axis provided in pin P. Bucket valve 199 is connected to bucket cylinder of the cylinder piston assembly 187 by conduits 193 and 194. Crowd valve 195 is connected to crowd cylinder of the cylinder and piston assembly 184 by conduits 196 and 197; and boom valve 200 is connected to boom cylinder of the cylinder and piston assembly 182 by conduitsl and 202. V

The control ports of the six control valves are interconnected by three port shuttle valves 'as used in FIG. 2 and function as previously described; although check valves could be used if limited flow attenuator means were added.

Shuttle valve 203 is connected to one bucket valve control port by conduit 204 and to one crowd valve control port by conduit 205. It can be seen that pressure applied to conduit 193 will curl the bucket and this working pressure will be applied to the control port at tached to conduit 204. In like manner, fluid pressure applied to crowd cylinder 184 through conduit 196 will retract crowd cylinder 184 drawing'bucketl85 toward pivot post in a digging cycle; and this pressure will be applied to the control port attached to conduit 205. Thus, shuttle 203 will select the higher of the two pressures involved in these digging operations and deliver the higher pressure to conduit 206 as control signal pressure B.

Control signal pressure B in conduit 206 is transmitted to the fluid responsive area of actuator 207 of mode valve 210 via conduit 211. At a predetermined pressure, actuator 207 overcomes the: load of spring 212, moving mode valve 210 from its first position, as shown, to a second position. In the second position, fluid pressure from conduit 213 is applied to boom cylinder 182 via conduit 214 to compress boom cylinder 182 and raise boom 181; thereby'decreasing the digging load incurred by the actuation of bucket cylinder 187 and crowd cylinder 184. During the raising of boom 181 by mode valve 210, excess fluid from boom cylinder 182 is exhausted through conduit 215 tosump 216.

The logic system of FIG. 5 includes ten shuttle valves in addition to shuttle valve 203. Control signalpressure B serves as one input for shuttle valve 220 and is applied to one input port of shuttle valve 220 via conduits 206 and 217. The output of all shuttle valves is taken from conduit 222 of shuttle valve 221. The 'fiuid pressure in conduit 222 is control signalpressure A; and

. this control signal pressure may be used to control the effective output of a fixed displacement pump as shown in FIG. 1 or a variable displacement pump as shown in FIG. 3.

It should be understood that anynumber of control ports may be interconnected by the use of shuttle valves to provide one, two or more flow reversible logic systems; and that the shuttle valves may be connected in various arrangements. These logic systems are made to be self-attenuating by cutting the lands of the valve spools back, as was described for lands 136a and 136b of FIG. 2.

The mode valve 230 shown in FIG. 6 is a variation of mode valve 210 of FIG. 5 inthat mode valve/230 is effective only to intercommunicate conduits2l4 and 215 with each other and with sump 216 thereby allowing boom 181 to float; whereas mode valve 210 power raises boom 181 to relieve excess digging pressures.

Various features of the invention have been particularly shown and described; however, it should be obvious to one skilled in the art that modifications may be made therein without departing from the scope of the invention.

What is claimed is:

1. In a hydraulic system including a source of fluid supply pressure comprising a pump, a sump, anda first delivery passage means providing a first working circuit including a first fluid-actuated device, and a first control valve connected to saidfirst device to control said first device; second delivery passage meansproviding a second working circuit including a second fluidactuated device, and a second control valve connected to said second device to control said second device;

a fluid pressure actuated mode valve in said second working circuit and operative to selectively modify the control of said second control valve over said second device in response to a control signal pressure applied to said mode valve;

control signal pressure supply means including conduit means, and mechanically actuated control signal occluder means, connected between said first control valve in said first circuit and said mode valve, and being effective to supply a working pressure from said first control valve to provide said control signal pressure, said occluder means being interposed between said conduit means and said first control valve, and operatively connected to said first control valve for actuation thereby to selectively block fluid communication from said first control valve to said conduit means and said mode valve;

and attenuator means connected to said conduit means and to said sump to provide a fluid flow path from said conduit means to said sump to attenuate said control signal pressure by allowing fluid to flow from said conduit means to said sump, and being effective to attenuate said control signal pressure only when said occluder means blocks fluid communication from said first control valve to said conduit means and said mode valve, said first control valve and said working pressure being effective to selectively control said mode valve, and said mode valve being effective to modify the control of said second control valve over said second device.

2. In a hydraulic system as defined in claim 1 wherein said attenuator means is operative to reduce the pressure level of said control signal pressure when said occluder means blocks fluid communication from said first control valve to said conduit means.

3. The system as defined in claim 1 in which said attenuator means includes valve means actuated by said first control valve to selectively establish and to selectively block communication between said sump and said conduit means.

4. The system as defined in claim 1 in which said mode valve is connected in series with said second control valve and said second fluid actuated device, said mode valve being effective to restrict the flow of fluid established between said second control valve and said second fluid actuated device by said second control valve.

5. The system as defined in claim 1 in which said mode valve is connected between said second fluid actuated device and in parallel with said control valve; said mode valve being effective to modify the flow of fluid to said second fluid actuated device independent of said second control valve.

6. The system as defined in claim 1 in which said mode valve includes first and second fluid responsive areas being adapted for differential pressure actuation of said mode valve to first and second operating positions by two fluid pressures; said control signal supply 8. The system as defined in claim 6 which includes hydraulically actuated threshold increaser means operably connected to said mode valve and adapted to increase said differential pressure required to actuate said mode valve in response to a fluid pressure applied to said threshold increaser means;

and a fluid conduit connecting said threshold increaser means to said source to obtain a fluid pressure therefrom.

9. The system defined in claim 1 which includes hydraulically actuated threshold increaser means operably connected to said mode valve and adapted to increase the magnitude of control signal required to actuate said mode valve in response to a fluid pressure applied to said threshold increaser means;

and a fluid conduit connecting said threshold increaser means to said source to obtain fluid pressure therefrom.

10. The system as claimed in claim 9 in which said threshold increaser includes piston and spring means.

11. In a hydraulic system as claimed in claim 1 in which said control signal supply means includes a control port in said first control valve, attenuator means, and conduit means and being adapted to connect said control valve to said mode valve, said control port supplying working pressure of said first device to said conduit means for use as said control signal pressure when said first control valve is supplying fluid from said source to said first device and being operative to occlude said working pressure of said first device from said conduit means when said first control valve is ineffective to supply fluid from said source to said first device, said attenuator means operatively interconnecting said conduit means and said sump and being operative to reduce the pressure level of said control signal when said control port occludes said working pressure from said mode valve, said first control valve and said working pressure being effective to control said mode valve and said mode valve being effective to modify the control of said second control valve over said second device.

12. The system as defined in claim 11 in which said first fluid actuated device includes first and second work ports, and said first control valve includes an inlet port connected to said source, a pair of exhaust ports connected to said sump, first and second work ports connected to said first and second work ports of said fluid actuated device, and said control signal supply means includes first and second control ports in said first control valve and fluid actuated poppet means, and said first control port communicating with said first work port and said second control port communicating with said second work port when said first control valve communicates said inlet'port with said second work port, and fluid actuated poppet means interposed between said control ports and said conduit means and being operative to selectively provide a fluid communication path from one of said control ports to said conduit means and to block fluid communication from said one control port to the other of said control ports.

13. The system as defined in claim 12 in which said fluid actuated poppet means includes a three port shuttle valve.

14. The system as defined in claim 13 in which said control valve includes a valve body having a spool bore and a valve spool slidably fitted in said spool bore; and said valve spool is movable from a neutral position to first and second operating positions to communicate said control ports to said exhaust ports when said valve spool is in said neutral position; and said three port shuttle valve having first and second input ports connected to said first and second control ports, an output port connected to said conduit means, and a poppet capable of blocking one or the other of said input ports, said control ports, said valve spool, and said shuttle valve cooperating to provide said attenuator means.

15. In a hydraulic system including a source of fluid pressure, a plurality of working circuits each including a fluid actuated device having at least one work port and each including a control valve having an inlet port and at least one work port, and a fluid sump, the improvement which comprises:

a pressure actuated mode valve interposed into a first of said working circuits which includes a first control valve and a first fluid actuated device, said mode valve being operative to modify the control of said first control valve over said first fluid actuated device in response to a control signal pressure applied to said mode valve;

control signal supply means including logic means and conduit means to select a working pressure from said two control valves for use as said control signal pressure;

said logic means including a plurality of control ports in said two control valves, fluid actuated poppet means, and attenuator means; each of said control ports being operatively associated with one of said work ports in said two control valves and connectible to one of said work ports by said two control valves, said fluid actuated poppet means connecting said control ports and said conduit means and being effective to select the highest working pressure from said control ports for use as said control signal pressure and to provide a fluid communication path to said conduit means; said conduit meansbeing operatively connected to said mode valve to supply said control signal pressure thereto, and

said attenuator means being operatively connected to said conduit means and to said sump and being effective to prevent a control signal pressure from being applied to said mode control valve that is higher than the highest fluid pressure in any of said work ports that are connected to said inlet port, whereby said two control valves and said working pressures therein are effective to control said mode valve and said mode valve is effectiveto modify the control of said first control valve over said first device.

16. The system as defined in claim 15 in which said fluid actuated poppet means includes a plurality of three port shuttle valves each having two input ports and one output port, and said output port of one of said shuttle valves is connected to one of said two input ports of another of said shuttle valves.

17. The system as defined in claim 15 in which said logic means is operative to select two control signal pressures from said working circuits and said control ports, one of said two control signal pressures being selected on the basis of the relative instantaneous working pressures in at least two of said control ports, and the working pressures in at least one of said control ports being used by said logic system in the selection of both of said two control signal pressures.

18. The system as defined in claim 17 in which one of said two control signal pressures. is connected to said mode valve for control thereof, and one of said two control signal pressures is operatively connected to said source and operative to control the effective output thereof.

19. The system as defined in claim 17 in which said hydraulic system includes threshold increaser means and in which said mode valve includes two fluid responsive areas for differential pressure actuation of said mode valve, one of said areas being operably connected to one of said two control signal pressures, the other of said areas being connected to said source, and said threshold increaser being operably connected to the other of said two control signal pressures.

20. The system as claimed in claim 19 in which said one control signal pressure is operatively connected to said source and is operative to control the effective output thereof. 

1. In a hydraulic system including a source of fluid supply pressure comprising a pump, a sump, and a first delivery passage means providing a first working circuit including a first fluidactuated device, and a first control valve connected to said first device to control said first device; second delivery passage means providing a second working circuit including a second fluid-actuated device, and a second control valve connected to said second device to control said second device; a fluid pressure actuated mode valve in said second working circuit and operative to selectively modify the control of said second control valve over said second device in response to a control signal pressure applied to said mode valve; control signal pressure supply means including conduit means, and mechanically actuated control signal occluder means, connected between said first control vAlve in said first circuit and said mode valve, and being effective to supply a working pressure from said first control valve to provide said control signal pressure, said occluder means being interposed between said conduit means and said first control valve, and operatively connected to said first control valve for actuation thereby to selectively block fluid communication from said first control valve to said conduit means and said mode valve; and attenuator means connected to said conduit means and to said sump to provide a fluid flow path from said conduit means to said sump to attenuate said control signal pressure by allowing fluid to flow from said conduit means to said sump, and being effective to attenuate said control signal pressure only when said occluder means blocks fluid communication from said first control valve to said conduit means and said mode valve, said first control valve and said working pressure being effective to selectively control said mode valve, and said mode valve being effective to modify the control of said second control valve over said second device.
 2. In a hydraulic system as defined in claim 1 wherein said attenuator means is operative to reduce the pressure level of said control signal pressure when said occluder means blocks fluid communication from said first control valve to said conduit means.
 3. The system as defined in claim 1 in which said attenuator means includes valve means actuated by said first control valve to selectively establish and to selectively block communication between said sump and said conduit means.
 4. The system as defined in claim 1 in which said mode valve is connected in series with said second control valve and said second fluid actuated device, said mode valve being effective to restrict the flow of fluid established between said second control valve and said second fluid actuated device by said second control valve.
 5. The system as defined in claim 1 in which said mode valve is connected between said second fluid actuated device and in parallel with said control valve; said mode valve being effective to modify the flow of fluid to said second fluid actuated device independent of said second control valve.
 6. The system as defined in claim 1 in which said mode valve includes first and second fluid responsive areas being adapted for differential pressure actuation of said mode valve to first and second operating positions by two fluid pressures; said control signal supply means being operably connected to one of said fluid responsive areas thereby supplying said control signal pressure thereto; and a fluid conduit connecting the other of said fluid responsive areas to said system to supply a fluid pressure from said system to said second area.
 7. The system as defined in claim 6 in which said second area is connected to said source.
 8. The system as defined in claim 6 which includes hydraulically actuated threshold increaser means operably connected to said mode valve and adapted to increase said differential pressure required to actuate said mode valve in response to a fluid pressure applied to said threshold increaser means; and a fluid conduit connecting said threshold increaser means to said source to obtain a fluid pressure therefrom.
 9. The system defined in claim 1 which includes hydraulically actuated threshold increaser means operably connected to said mode valve and adapted to increase the magnitude of control signal required to actuate said mode valve in response to a fluid pressure applied to said threshold increaser means; and a fluid conduit connecting said threshold increaser means to said source to obtain fluid pressure therefrom.
 10. The system as claimed in claim 9 in which said threshold increaser includes piston and spring means.
 11. In a hydraulic system as claimed in claim 1 in which said control signal supply means includes a control port in said first control valve, attenuator means, and conduit means and being adapted to connect said Control valve to said mode valve, said control port supplying working pressure of said first device to said conduit means for use as said control signal pressure when said first control valve is supplying fluid from said source to said first device and being operative to occlude said working pressure of said first device from said conduit means when said first control valve is ineffective to supply fluid from said source to said first device, said attenuator means operatively interconnecting said conduit means and said sump and being operative to reduce the pressure level of said control signal when said control port occludes said working pressure from said mode valve, said first control valve and said working pressure being effective to control said mode valve and said mode valve being effective to modify the control of said second control valve over said second device.
 12. The system as defined in claim 11 in which said first fluid actuated device includes first and second work ports, and said first control valve includes an inlet port connected to said source, a pair of exhaust ports connected to said sump, first and second work ports connected to said first and second work ports of said fluid actuated device, and said control signal supply means includes first and second control ports in said first control valve and fluid actuated poppet means, and said first control port communicating with said first work port and said second control port communicating with said second work port when said first control valve communicates said inlet port with said second work port, and fluid actuated poppet means interposed between said control ports and said conduit means and being operative to selectively provide a fluid communication path from one of said control ports to said conduit means and to block fluid communication from said one control port to the other of said control ports.
 13. The system as defined in claim 12 in which said fluid actuated poppet means includes a three port shuttle valve.
 14. The system as defined in claim 13 in which said control valve includes a valve body having a spool bore and a valve spool slidably fitted in said spool bore; and said valve spool is movable from a neutral position to first and second operating positions to communicate said control ports to said exhaust ports when said valve spool is in said neutral position; and said three port shuttle valve having first and second input ports connected to said first and second control ports, an output port connected to said conduit means, and a poppet capable of blocking one or the other of said input ports, said control ports, said valve spool, and said shuttle valve cooperating to provide said attenuator means.
 15. In a hydraulic system including a source of fluid pressure, a plurality of working circuits each including a fluid actuated device having at least one work port and each including a control valve having an inlet port and at least one work port, and a fluid sump, the improvement which comprises: a pressure actuated mode valve interposed into a first of said working circuits which includes a first control valve and a first fluid actuated device, said mode valve being operative to modify the control of said first control valve over said first fluid actuated device in response to a control signal pressure applied to said mode valve; control signal supply means including logic means and conduit means to select a working pressure from said two control valves for use as said control signal pressure; said logic means including a plurality of control ports in said two control valves, fluid actuated poppet means, and attenuator means; each of said control ports being operatively associated with one of said work ports in said two control valves and connectible to one of said work ports by said two control valves, said fluid actuated poppet means connecting said control ports and said conduit means and being effective to select the highest working pressure from said control ports For use as said control signal pressure and to provide a fluid communication path to said conduit means; said conduit means being operatively connected to said mode valve to supply said control signal pressure thereto, and said attenuator means being operatively connected to said conduit means and to said sump and being effective to prevent a control signal pressure from being applied to said mode control valve that is higher than the highest fluid pressure in any of said work ports that are connected to said inlet port, whereby said two control valves and said working pressures therein are effective to control said mode valve and said mode valve is effective to modify the control of said first control valve over said first device.
 16. The system as defined in claim 15 in which said fluid actuated poppet means includes a plurality of three port shuttle valves each having two input ports and one output port, and said output port of one of said shuttle valves is connected to one of said two input ports of another of said shuttle valves.
 17. The system as defined in claim 15 in which said logic means is operative to select two control signal pressures from said working circuits and said control ports, one of said two control signal pressures being selected on the basis of the relative instantaneous working pressures in at least two of said control ports, and the working pressures in at least one of said control ports being used by said logic system in the selection of both of said two control signal pressures.
 18. The system as defined in claim 17 in which one of said two control signal pressures is connected to said mode valve for control thereof, and one of said two control signal pressures is operatively connected to said source and operative to control the effective output thereof.
 19. The system as defined in claim 17 in which said hydraulic system includes threshold increaser means and in which said mode valve includes two fluid responsive areas for differential pressure actuation of said mode valve, one of said areas being operably connected to one of said two control signal pressures, the other of said areas being connected to said source, and said threshold increaser being operably connected to the other of said two control signal pressures.
 20. The system as claimed in claim 19 in which said one control signal pressure is operatively connected to said source and is operative to control the effective output thereof. 